The present invention relates to a linear-gain amplifier arrangement which comprises a current-amplifying cell comprising a first and a second current-mirror circuit. The first and second current-mirror circuits each comprise at least an input transistor and an output transistor to form a first and a second differential pair respectively. Means coupled to the current-amplifying cell are provided to define the gain of the amplifier arrangement.
An amplifier arrangement of this type, comprising bipolar transistors, is described, inter alia, in "A New Wide-Band Amplifier Technique" by B. Gilbert, IEEE Journal of Solid State Circuits, vol. SC-3, no. 4, Dec. 1968, pp. 353-365.
In the technology of electronically amplifying electric signals it is generally known that the bandwidth of an amplifier arrangement can be extended by applying negative feedback. However, a problem which arises when negative feedback is applied to amplifiers is the trade-off that is required between the bandwidth and the linearity of the transfer function. This is because the amplifier arrangement tends to become less stable as the bandwidth is extended by reason of the increased negative feedback. Conversely, open-loop amplifier arrangements which do not employ any form of negative feedback whatsoever have an excellent linearity without a trade-off in the bandwidth of the amplifier arrangement.
The bipolar amplifier arrangement defined in the opening paragraph is of the type without negative feedback and has a wide-band frequency response, a desired linear transfer characteristic, and an electronically controllable gain. These properties make the amplifier arrangement very suitable for use where bipolar amplifier arrangements with a linear gain at high frequencies beyond 100 MHz are required.